While video streaming continues to grow in popularity and usage among everyday users, there are several inherent limitations that need to be overcome. For example, users often want to watch a video over the Internet having only a limited bandwidth for obtaining that video stream. In instances, users might want to obtain the video stream over a mobile telephone connection or a home wireless connection. In some scenarios, users compensate for the lack of adequate bandwidth by spooling content (i.e., download content to local storage for eventual viewing). This method is rife with several disadvantages. First, the user is unable to have a real “run-time” experience—that is, the user is unable to view a program when he decides to watch it. Instead, he has to experience significant delays for the content to be spooled prior to viewing the program. Another disadvantage is in the availability of storage—either the provider or the user has to account for storage resources to ensure that the spooled content can be stored, even if for a short period of time, resulting in unnecessary utilization of expensive storage resources.
A video stream (typically containing an image portion and an audio portion) can require considerable bandwidth, especially at high resolution (e.g., HD videos). Audio typically requires much less bandwidth, but still sometimes needs to be taken into account. One streaming video approach is to heavily compress the video stream enabling rapid video delivery to allow a user to view content in run-time or substantially instantaneously (i.e., without experiencing substantial spooling delays). Typically, lossy compression (i.e., compression that is not entirely reversible) provides more compression than lossless compression, but heavy lossy compression provides an undesirable user experience.
In order to reduce the bandwidth required to transmit digital video signals, it is well known to use efficient digital video encoding where the data rate of a digital video signal may be substantially reduced (for the purpose of video data compression). In order to ensure interoperability, video encoding standards have played a key role in facilitating the adoption of digital video in many professional- and consumer applications. Most influential standards are traditionally developed by either the International Telecommunications Union (ITU-T) or the MPEG (Motion Pictures Experts Group) 15 committee of the ISO/IEC (the International Organization for Standardization/the International Electrotechnical Committee. The ITU-T standards, known as recommendations, are typically aimed at real-time communications (e.g. videoconferencing), while most MPEG standards are optimized for storage (e.g. for Digital Versatile Disc (DVD>> and broadcast (e.g. for Digital Video Broadcast (OVB) standard).
At present, the majority of standardized video encoding algorithms are based on hybrid video encoding. Hybrid video encoding methods typically combine several different lossless and lossy compression schemes in order to achieve desired compression gain. Hybrid video encoding is also the basis for ITV-T standards (H.26x standards such as H.261, H.263) as well as ISO/IEC standards (MPEG-X standards such as MPEG-1, MPEG-2, and MPEG-4). The most recent and advanced video encoding standard is currently the standard denoted as H.264/MPEG-4 advanced video coding (AVC) which is a result of standardization efforts by joint video team (JVT), a joint team of ITV-T and ISO/IEC MPEG groups.
The H.264 standard employs the same principles of block-based motion compensated hybrid transform coding that are known from the established standards such as MPEG-2. The H.264 syntax is, therefore, organized as the usual hierarchy of headers, such as picture-, slice- and macro-block headers, and data, such as motion-vectors, block-transform coefficients, quantizer scale, etc. However, the H.264 standard separates the Video Coding Layer (VCL), which represents the content of the video data, and the Network Adaptation Layer (NAL), which formats data and provides header information.
Furthermore, H.264 allows for a much increased choice of encoding parameters. For example, it allows for a more elaborate partitioning and manipulation of 16×16 macro-blocks whereby e.g. motion compensation process can be performed on segmentations of a macro-block as small as 4×4 in size. Also, the selection process for motion compensated prediction of a sample block may involve a number of stored previously-decoded pictures, instead of only the adjacent pictures. Even with intra coding within a single frame, it is possible to form a prediction of a block using previously-decoded samples from the same frame. Also, the resulting prediction error following motion compensation may be transformed and quantized based on a 4×4 block size, instead of the traditional 8×8 size. Additionally, an in-loop deblocking filter that reduces block artifacts may be used.
The H.264 standard may be considered a superset of the H.262/MPEG-2 video encoding syntax in that it uses the same global structuring of video data while extending the number of possible coding decisions and parameters. A consequence of having a variety of coding decisions is that a good trade-off between the bit rate and picture quality may be achieved. However, although it is commonly acknowledged that while the H.264 standard may significantly reduce typical artifacts of block-based coding, it can also accentuate other artifacts. The fact that H.264 allows for an increased number of possible values for various coding parameters thus results in an increased potential for improving the encoding process, but also results in increased sensitivity to the choice of video encoding parameters.
Similar to other standards, H.264 does not specify a normative procedure for selecting video encoding parameters, but describes through a reference implementation, a number of criteria that may be used to select video encoding parameters such as to achieve a suitable trade-off between coding efficiency, video quality and practicality of implementation. However, the described criteria may not always result in an optimal or suitable selection of coding parameters suitable for all kind of contents and applications. For example, the criteria may not result in selection of video encoding parameters optimal or desirable for the characteristics of the video signal or the criteria may be based on attaining characteristics of the encoded signal which are not appropriate for the current application.
Accordingly, an improved system for video encoding would be advantageous.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.